1. Field of the Invention
The present invention relates to a method for assembling a power transfer apparatus for secondary driving wheels of a four-wheel drive vehicle.
2. Description of the Related Art
In conventional four-wheel drive vehicles, in turning a corner of a small turning radius at low or middle speed in a four-wheel drive mode, there is caused a difference in wheel speed between front and rear wheels which is attributed to a difference in turning radius between the front and rear wheels, resulting in the occurrence of a tight corner braking phenomenon.
Front and rear wheels driving systems disclosed in JP-B-7-61779 and JP-B-7-64219 are known as related arts for solving the problem of tight corner braking phenomenon.
In the front and rear wheel driving systems disclosed in the Japanese Examined Patent Publications, an average wheel speed of secondary driving wheels relative to an average wheel speed of primary driving wheels is adjusted by providing a transmission (a speed increasing apparatus) between the primary and secondary driving wheels.
In this transmission, by switching on and off a direct clutch and a transmission clutch or vice versa, there occurs a changeover between a direct connecting mode in which the average wheel speed of the primary driving wheels and the average wheel speed of the secondary driving wheels are almost equalized and a speed increasing mode in which the average wheel speed of the secondary driving wheels is made larger than the average wheel speed of the primary driving wheels.
In this front and rear wheel driving system, when turning a small corner in the four-wheel drive mode, the occurrence of tight corner braking phenomenon is prevented by bringing the secondary driving wheels in the speed increasing mode by the transmission.
Incidentally, in the aforesaid transmission (the speed increasing apparatus) for four-wheel drive vehicles, at least two hydraulic or electromagnetic actuators are required as a power source for actuating the direct clutch and the transmission clutch, and this leads to a problem that the transmission itself is made larger in size and hence heavier in weight.
Furthermore, since this transmission is such as to be constructed by assembling constituent components piece by piece in the assembling process of the transmission, the number of processes is increased and hence the productivity is deteriorated. In addition, since there are many items needing adjustments such as clearance and spring load, the productivity is also deteriorated.